This invention relates generally to the development of biocides used in wood preservation, and more particularly to the discovery that a polymer with pendant groups containing pyridine rings complexed with copper is effective as a treatment for wood for preservation purposes.
The history of man's efforts at wood preservation is a long one, dating back several thousands of years to the first coating of wood with oils to increase its durability. Ironically, the principal methods and materials employed by the wood preservation industry have changed relatively slowly over the years. For example, the major biocidal preservatives in use today are creosote, pentachlorophenol and chromated copper arsenates (CCAs), which were patented in 1834, the late 1920's and 1933, respectively. Moreover, with pressure treating of wood products still being the most practiced technique, it is interesting that common pressure processes still in use today, such as the full-cell process and the Lowry empty-cell process, were patented between 1838 and 1906.
Looking more carefully for the moment at the wood-attacking fungi and bacteria themselves, hundreds of different species have been isolated over the years which attack wood products in one of many ways. These effects range from complete destruction to deep or surface staining and even to no apparent effect in certain instances. Typical varietal classes for the wood-attacking fungi include surface molds, sap stain fungi, decay fungi, soft-rot fungi and others. Typical wood-attacking bacteria include Sarcina lutea, Pseudomonas nigrifaciens, and other soil and marine bacteria. Disregarding their many differences, all have in common five basic requirements to survive, those being the need for food, oxygen (in some cases), moisture, warmth and a suitable pH. Nonbiocidal techniques, designed to control these organisms by modifying or eliminating any one of these environmental requirements, are available and have met with degrees of success under certain circumstances. However, biocidal wood preservatives have been long regarded as the most effective and commonly used control method.
Research directed to the formulation of new biocides for fungicidal and bacteriacidal uses is a long and arduous task. Added to the normal costs of research and development must be the stringent requirements of governmental controls, considerations of the environment, the universal roles these substances must fill, and the like. For example, a listing of suggested requirements for an effective wood preservative formulation would need to include: (1) that it be toxic to wood-attacking fungi and bacteria, and possibly also to a wide variety of insects such as termites, Lyctide, Anobiid, and Cerambycide beetles; (2) that it has sufficient permanence to provide an acceptable useful life for the wood; (3) that it have little, if any, effect on the strength or other properties of the wood; (4) that it provide good penetration into the wood depending on the method of application used; (5) that it be readily available and relatively inexpensive and easy to apply; and (6) that the wood after treatment be safe to handle, nontoxic to other animal and plant life, noncorrosive to fastening means or other materials which contact it, and at least for certain applications be paintable, odorless, colorless, water-repellant, compatible with various adhesives and like considerations.
As for the types of biocides now used for wood preservation, these typically fall within two categories . . . oil-borne preservatives (of which pentachlorophenol and distillates of coal tar such as creosotes are most common) and water-borne preservatives (of which copper-containing inorganic salt-type biocides such as acid copper chromate (ACC), chromated copper arsenate (CCA) and ammoniacal copper aresenate (ACA) are common examples). For a listing of other known biocides, and particularly fungicides, and for a good general discussion of the entire wood preservation industry, reference can be made to M. P. Levi, "Fungicides in Wood Preservation," Antifungal Compounds, Vol. 1, edited by M. R. Siegel and H. D. Sisler, Marcel Decker, Inc., 397-436 (1977).
Although the primary concern in wood preservation is prevention of decay, control of surface mold growth and other more superficial considerations are also of importance, particularly in a given environment. The mode of action of biocides on the market and their effectiveness in dealing with wood-attacking fungi and bacteria in a given situation is often tied to the method of application used. In this regard, long thought to be most reliable for commercial preservation purposes has been pressure treatment techniques particularly when seasoned wood is involved. Vacuum treatments, hot and cold bath or thermal treatments, cold-soak treatments and more superficial treatments such as brushing, spraying, dipping or short-soak methods are also practiced with seasoned woods. Diffusion treatments, sap displacements and similar superficial treatments are most common when unseasoned wood is involved. The article by M. P. Levi mentioned above provides good discussion of these application methods including their advantages and disadvantages under particular circumstances.
In the past two-to-three-year period, a few publications have addressed the possible biocidal properties of specific polymeric compounds. These have consisted of certain polymeric quaternary salts [I. H. Walfish and G. E. Janauer, Water, Air and Soil Pollution, 12, 477 (1979)] and polymers that contain halogens such as iodine [L. R. Fina, Ind. Eng. Chem. Prod. Res. Dev., 19, 259 (1980)]. Their suggested uses have principally been to control bacteria in water. In only one instance known to applicant has a polymer been reported as having possible use in wood preservation [Charles E. Carraher, Jr. and Charles G. Gebelein, Biological Activities of Polymers, 28-33 (1982)]. The polymers tested were two organometallic polymers which had been previously developed, tributyltin methacrylate/methyl methacrylate copolymer and the tributyltin ester of methyl vinyl ether/maleic anhydride.